This is a simple curtain ring, fully parametric.
You can either use the STL provided, which will give you a 75mm diameter ring, with a 10mm thickness, or you can edit the OpenSCAD Source to your own preferences.
Printing is a bit of an issue, the photos attached were printed with a small 6 ring raft 1mm away from the print. The results were not, as you can see, perfect. Surprisingly my spouse was happy with the results and I have been given the go-ahead to print the rest.
The .scad file has the ability to lower the print by the amount specified in zcrop, say 0.3mm, which might make it a little easier to print, at a cost of symmetry.
Anyway, see the photo attached and you can decide for yourself which way you would like to go. Please do add comments with your feedback.